刚刚装好的虚拟机突然不能上网了，报错很诡异，具体报错如下：
/etc/init.d/network restart
Restarting network (via systemctl): Job for network.service failed because the control process exited with error code. See "systemctl status network.service" and "journalctl -xe" for details.
[失败]
使用systemctl status network.service命令查看结果如下：
network.service - LSB: Bring up/down networking
Loaded: loaded (/etc/rc.d/init.d/network)
Active: failed (Result: exit-code) 54s ago
Docs: man:systemd-sysv-generator(8)
Process: 3847 ExecStart=/etc/rc.d/init.d/network start (code=exited, status=1/FAILURE)
python.cn network[3847]: RTNETLINK answers: File exists
python.cn network[3847]: RTNETLINK answers: File exists
python.cn network[3847]: RTNETLINK answers: File exists
python.cn network[3847]: RTNETLINK answers: File exists
python.cn network[3847]: RTNETLINK answers: File exists
python.cn network[3847]: RTNETLINK answers: File exists
python.cn systemd[1]: network.service: control process exited, code=exited status=1
python.cn systemd[1]: Failed to start LSB: Bring up/down networking.
python.cn systemd[1]: Unit network.service entered failed state.
python.cn systemd[1]: network.service failed.
查看系统日志，报错如下：
python network: RTNETLINK answers: File exists
python network: RTNETLINK answers: File exists
python network: RTNETLINK answers: File exists
python network: RTNETLINK answers: File exists
python network: RTNETLINK answers: File exists
python network: RTNETLINK answers: File exists
python network: RTNETLINK answers: File exists
python network: RTNETLINK answers: File exists
python network: RTNETLINK answers: File exists
python systemd: network.service: control process exited, code=exited status=1
python systemd: Failed to start LSB: Bring up/down networking.
python systemd: Unit network.service entered failed state.
python systemd: network.service failed.
Aug 17 11:36:28 python systemd: Starting LSB: Bring up/down networking...
python network: 正在打开环回接口： 无法载入文件 '/etc/sysconfig/network-scripts/ifcfg-lo'
python network: 无法载入文件 '/etc/sysconfig/network-scripts/ifcfg-lo'
python network: 无法载入文件 '/etc/sysconfig/network-scripts/ifcfg-lo'
python network: 无法载入文件 '/etc/sysconfig/network-scripts/ifcfg-lo'
python network: [ 确定 ]
python network: 正在打开接口 eno16777736： 错误：激活连接失败：No suitable device found for this connection.
经查，确认/etc/sysconfig/network-scripts/ifcfg-lo文件是存在的。问题出现在哪里呢？无法，只好搜索一下吧，搜索出来的结果竟然基本一样。
答案：
mac地址不对，修改mac地址。
也许有人确实是mac问题，但是莫名其妙怎么可能mac地址更改了，除非你添加新网卡或者克隆的虚拟机。
以上为搜索出来的办法。
没办法了，再找一下文章，偶然看到一个文章，大意是跟系统自带的NetworkManager这个管理套件有关系，关掉就可以解决。
试一下：
systemctl stop NetworkManager
systemctl disable NetworkManager
Removed symlink /etc/systemd/system/multi-user.target.wants/NetworkManager.service.
Removed symlink /etc/systemd/system/dbus-org.freedesktop.NetworkManager.service.
Removed symlink /etc/systemd/system/dbus-org.freedesktop.nm-dispatcher.service.
重新启动网络：
systemctl start network.service
ifconfig |grep eno
eno16777736: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.192 netmask 255.255.255.0 broadcast 192.168.1.255
inet6 fe80::20c:29ff:fe3d:b305 prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:3d:b3:05 txqueuelen 1000 (Ethernet)
RX packets 2 bytes 120 (120.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 22 bytes 3551 (3.4 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
网络正常启动，访问正常。